The present invention relates, in general, to integrated circuits and, more particularly, to current limiting circuits.
A portable wireless system such as a cellular phone or a pager uses analog and active circuitry to convert signals between frequencies ranging from radio frequency (RF) to base band. Received RF signals are converted to base-band signals through circuits such as an RF transceiver, a down converter, and a demodulator. In the case of a cellular phone, the converted base-band signals are processed into recognizable speech in the voice band frequencies. The portable wireless system typically draws its operating power from a battery source. Analog and active circuitry in the portable wireless system are primary sources of battery current drain during system operation.
The transistors of the analog and active circuitry have well regions formed in a substrate of the integrated circuit. The reverse-biased PN-junction diodes formed by the well regions in the substrate have leakage currents based on the junction area of the diodes. When the portable wireless system is not transmitting or receiving signals the system enters a standby mode to prolong battery life. In standby mode a majority of the analog and active circuitry is disabled which causes the diode leakage currents to be the dominant current that diminishes the life of the battery.
Accordingly, it would be advantageous to have a circuit that limits the diode leakage currents of an integrated circuit during a standby mode to prolong the battery life of a portable wireless system. It would be of further advantage that the current limiting circuit have a small size and be easily integrated.